[Linux-cluster] CMAN/DLM without SCTP

Christine Caulfield ccaulfie at redhat.com
Tue Feb 18 13:48:10 UTC 2014

On 18/02/14 13:33, Pratik Mehta wrote:
> Hi,
> I am trying to use a cluster with Pacemaker + CMAN on CentOS 6.4. The
> application that runs on the cluster includes a userspace SCTP stack.
> However CMAN loads dlm which loads the Linux kernel sctp module, which
> interferes with the userspace SCTP.
> I do not have any GFS/locking requirements on this cluster. I use a 2
> node cluster to failover a bunch of IP addresses.
> I tried setting DLM_CONTROLD_OPTS="-r 0" and blacklisting sctp module.
> Didn't help since dlm depends on sctp and cman loads dlm.
> In /etc/init.d/cman:
> errmsg=$( modprobe dlm 2>&1 ) || return 1
> errmsg=$( modprobe lock_dlm 2>&1 ) || true
> As a hack: I modified the cman service to not load dlm and lock_dlm. The
> cluster seems working. However I do not know what additional
> functionality was broken when I disabled these. Though a hack: I am
> eager to know if someone sees an issue of running a production cluster
> with this.
> Another options is to introduce a compile time flag in the DLM kernel
> module to not use SCTP.
> Is there any other way?

You should be fine like that. The things that use the DLM are GFS and 
clvmd so if you don't use either of those then not having the DLM 
running won't have any effect. You'd soon see error messages if anything 
you were running depended on it .. I hope!

I suppose we didn't really envisage alternative SCTP stacks when the DLM 
was written and it's never come up as a problem before.


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